This patent relates to a process to convert slivers and fines (referred to as "SWARF" in the industry) from refractory metal (titanium and zirconium metal) grinding operations into a consolidated, safe to handle, raw material suitable for aluminum, magnesium and iron refractory metal alloys and master alloys, such as aluminum-titanium alloys, magnesium-zirconium alloys, aluminum-zirconium alloys, iron-titanium alloys, iron-zirconium alloys, aluminum-titanium-boron alloys, and the like. At present, most refractory metal products are produced from large ingots, which involve various hot forging and rolling operations. Whenever refractory metals are heated above about 700.degree. C. in air, refractory metal oxides and nitrides are formed with large heat release varying in thickness depending on both the temperature and time. Most of the oxide is removed by mechanical means, usually sand or bead blasting. However, some of the oxide is in the form of pits which projects more deeply than average into the base metal and is not removed by these operations. The pits are usually removed by belt grinding processes in which a silicon carbide, aluminum-zirconium oxide, or other hard grit, typically about 60 mesh, bonded to a belt is moved over the surface of the metal, removing a mil to several mils of the surface per pass in the form of small curved slivers of the refractory metal. The belt grinding machine gouges the slivers of metal with each of the individual grains of grit on the belt. These fine slivers of refractory metal in bulk are called "SWARF" in the industry. The amount of SWARF generated is perhaps on the order of one percent of the weight of the metal piece being processed, depending on the thickness of refractory metal being ground. Belt grinding is also used to obtain flat surfaces on refractory metal plates and slabs and to obtain rounded surfaces on rods an other round objects.
Refractory metal particles are also produced by other abrasive operations, such as grinding with abrasive wheels or stone grinding using copious coolant. For purposes of this invention, these refractory metal particles are suitable for use in the present invention and will be understood to be included within the term "SWARF". The refractory metal particles produced from stone or abrasive wheel grinding is typically sent to a settling tank with the coolant and allowed to settle to the bottom of the tank. The coolant is recycled.
At the present time, SWARF is considered a waste product and is disposed of by burning in the open air at a remote site. SWARF has a very low ignition point and is highly pyrophoric; it combusts suddenly and violently with the rapidity and brightness of a photographic flashbulb to produce a very hazardous fire. Accordingly, SWARF must be maintained under water or under a non-oxidizing environment to reduce reaction with N.sub.2 and O.sub.2 in the air. This burn operation generates a thick white smoke (TiO.sub.2) or (ZrO.sub.2) and is receiving increasing scrutiny from regulatory agencies.
The existing grinding operations are conducted with water or a non-flammable grinding fluid (collectively "grinding fluid"). The SWARF is removed from the grinder mechanically along with the grinding fluid. The SWARF and grinding fluid frequently go through an initial screening wherein the coarse SWARF is separated from the bulk of the fines SWARF and the grinding fluid. The SWARF fines and grinding fluid are sent to a filter wherein the SWARF fines are separated from the grinding fluid. The grinding fluid is recycled back to the grinding operation. The coarse SWARF and fine SWARF are combined and disposed of by burning.
The grinding fluid usually contains components to aid in continuously cleaning the SWARF from grinding media and fire retardants. These components also unfortunately add chemical impurities to the SWARF material tending to further limit its value.
The refractory metals titanium and zirconium are made from relatively cheap and plentiful ores. The extraction, purification and consolidation of these metals is, however, expensive. Thus the metallic value in the SWARF after its removal during grinding is sufficient to warrant recovery if it can be reprocessed to eliminate its hazardous, pyrophoric nature and cleaned of components detrimental to potential end uses.